Research on developing the new machine, Legged vehicle, is on-going to mechanize forest operation, especially silvicultural operation, on steep, difficult sites. The machine developed on 1991, has 2 knuckle boom type legs on front and 4 pantograph type legs on rear which are driven by hydraulic cylinders. The machine is controlled by multi CPU system, the 6 legs are controlled independently by 6 CPU units and the other CPU unit controls the 6 CPU units.Improving the machineThe weak parts were reinforced.Discussion on the control systemSimulation experiments were made with small model. The control system for walking with 6 legs synchronizing each other was discussed on.Improving the control softwareThe algorithms and the communication protocols to synchronize different type legs, 2 knuckle boom type legs on front and 4 pantograph type legs on rear, were discussed on. The experiment with this software made good results.Possibility of the machine for forest operationFrom the discussion on the operator's Physiological reaction, it was cleared that the traditional vehicle's operator was stressed by terrain roughness. If the legged machine could walk without effect of terrain roughness, the operator's stress on forest operations would decrease.